1. Field of the Disclosure
The present disclosure relates to a liquid crystal display device, and more particularly, to an array substrate where problems due to shifts of column spacers are prevented and a liquid crystal display device including the same.
2. Discussion of the Related Art
A liquid crystal display device has been widely used in various electronics, such as a notebook, a monitor, a TV, etc., since it has a high contrast ratio, is suitable to display moving images, and has low consumption power. Liquid crystal has optical anisotropy in which its molecular structure is thin and long and its molecular arrangement has directivity, and has polarization in which the direction of its molecular arrangement changes according to the magnitude of an electric field when the liquid crystal is in the electric field. The liquid crystal display device displays images using the optical anisotropy and polarization of liquid crystal.
In general, a liquid crystal display device includes a liquid crystal panel fabricated by bonding first and second substrates with a liquid crystal layer therebetween, and electrodes are formed on the facing surfaces of the first and second substrates so that the arrangement of liquid crystal molecules depends on an electric field applied to the electrodes to thereby make a difference in transmittance.
The difference in transmittance of the liquid crystal panel is reflected in a combined color when light emitted from a backlight positioned on the rear side of the liquid crystal panel passes through a color filter, thereby representing a color image.
A method of fabricating a liquid crystal display device includes a substrate fabricating process of forming an array substrate and a color filter substrate, a cell process of fabricating a liquid crystal panel, and a module process of integrating the liquid crystal panel with a backlight.
In the substrate fabricating process, steps of thin film deposition, photolithography, etching, etc., are repeatedly performed to form an array layer and a color filter layer on the respective substrates. In the cell process, a seal pattern for bonding is formed on one of the array substrate and the color filter substrate, and the array substrate is bonded to the color filter substrate with the liquid crystal layer interposed therebetween to thereby fabricate the liquid crystal panel. In the module process, a polarizer, a driving circuit, etc. are attached onto the liquid crystal panel and then the liquid crystal panel is integrated with the backlight to thereby complete a liquid crystal display device.
Meanwhile, spacers are provided between the array substrate and the color filter substrate in order to maintain a constant distance between the array substrate and the color filter substrate. The spacers are classified into ball spacers and column spacers according to their shapes and arrangement. The ball spacers are formed in such a manner to be distributed on the array substrate or the color filter substrate, and the column spacers are formed through patterning on the array substrate or the color filter substrate.
Recently, column spacers have been widely used since they can be easily formed in a desired pattern at a specific location, and the column spacers are formed generally on a color filter substrate requiring a relatively small number of processes.
However, when an external force is applied to a liquid crystal panel, column spacers move, which damages an alignment layer and causes defects. This will be described in detail with reference to a drawing.
FIG. 1 is a cross-sectional view of a related art liquid crystal display device.
In FIG. 1, a first substrate 10 and a second substrate 20 are spaced apart from and faces each other with a distance therebetween, and an aperture area AA in which an image is displayed and a shielding area SA in which no image is displayed are defined on the first substrate 10 and the second substrate 20.
On an inner surface of the first substrate 10 facing the second substrate 20, a signal line 12, such as a gate line or a data line, is formed in correspondence to the shielding area SA, an insulating layer 14 is formed on the signal line 12, and a first alignment layer 16 is formed on the insulating layer 14. Although not shown in FIG. 1, a pixel electrode is formed in the aperture area AA on the first substrate 10.
On an inner surface of the second substrate 20 facing the first substrate 10, a black matrix 22 is formed, a color filter layer 24 is formed on the black matrix 22, and a second alignment layer 26 is formed on the color filter layer 24. Although not shown in FIG. 1, a common electrode is formed on the entire surface of the second substrate 20. Also, a column spacer 32 is formed on the second alignment layer 26, in correspondence to the black matrix 22, such that at least one column spacer 32 is formed for each pixel.
Meanwhile, a liquid crystal layer (not shown) is positioned between the first alignment layer 16 and the second alignment layer 26.
FIGS. 2A and 2B are cross-sectional views of the related art liquid crystal display device when an external force is applied to the related art liquid crystal display device and when the applied external force is removed.
In FIG. 2A, when an external force is applied to the related art liquid crystal display device in the direction of an arrow shown in FIG. 2A, the second substrate 20 moves to the right with respect to the first substrate 10. At this time, the column spacer 32 on the second substrate 20 also moves to the right, so that the column spacer 32 contacts the first alignment layer 16 of the aperture area AA. The first and second alignment layers 16 and 26 are rubbed or optically aligned in a predetermined direction, and due to the contact with the column spacer 32, the alignment of the first alignment layer 16 changes at a contact area A1 so that the contact area A1 has different alignment from the other area.
Successively, in FIG. 2B, when the external force is removed, the second substrate 20 moves to the left with respect to the first substrate 10 to return to its original state. However, since the contact area A1 of the first alignment layer 16 has a different alignment from the other area, liquid crystal molecules over the contact area A1 are aligned differently from liquid crystal molecules over the other area to thereby change transmittance of light. However, since the contact area A1 is not covered by the black matrix 22, light is transmitted in correspondence to the contact area A1 when a black image is displayed, resulting in a recognizable defect.
A structure for preventing such a defect is shown in FIG. 3.
FIG. 3 is a cross-sectional view of another related art liquid crystal display device. The structure shown in FIG. 3 is the same as that shown in FIG. 1, except for the structure of the black matrix. In the following description, the same elements as those described above will not be described.
In FIG. 3, a width of each black matrix 22 increases to a predetermined size such that the black matrix 22 covers the contact area A1 of the first alignment layer 16. In detail, the width of the black matrix 22 increases to a predetermined size in which the black matrix 22 extends to about 22 to 25 micrometers from both top edges of the column spacer 32 contacting the first alignment layer 16. That is, the width of the black matrix 22 increases by about 15 micrometers or more, compared to the black matrix 22 of the example shown in FIG. 1.
However, the increased width of the black matrix 22 increases the shielding area SA to reduce the aperture areas AA, which lowers the aperture ratio and brightness of the liquid crystal display device.